1. Field of the Invention
The invention relates to a Coriolis mass flowmeter having at least four measuring tubes running parallel, wherein the measuring tubes are joined in pairs into an oscillation unit by at least one holding device, wherein the measuring tubes are inserted in openings in the holding device and wherein at least part of either a sensor or an actuator device is attached to the holding device.
2. Description of Related Art
Mass flowmeters that function according to the Coriolis principal generally have at least one actuator device with which the measuring tube or the oscillation units are excited to oscillation as well as normally two sensor devices, with which the desired oscillation or the desired oscillations of the measuring tube is/are detected. The sensor devices are normally mounted to the oscillation units on the input and output sides. Without flow, both signals have essentially the same phase. During mass flow, a phase shift of both signals results from the different Coriolis forces during feed and discharge, which is proportional to the mass flow so that this can be determined by the phase shift.
The actuator device and the sensor device are normally arranged in such a manner that they, for example, have a permanent magnet as well as a magnet coil, in order to transfer oscillations to the measuring tube electrically—action of force—or to detect oscillations of the measuring tube—inductive effect. The applicant knows of mass flowmeters with four measuring tubes from practice, in which each two measuring tubes are joined to an oscillation unit with at least one holding device, which are excited to oscillation by an actuator device. The known Coriolis mass flowmeters, however, have the disadvantage that the measuring tubes of an oscillation unit do not oscillate only in relation to the other oscillation units, but the measuring tubes of an oscillation unit can also oscillate in relation to one another, through which the measurements of the Coriolis mass flowmeter are negatively influenced.